title: Miniaturization of two-photon microscopy for imaging in freely moving animals.
abstract: This article describes the development and application of miniaturized two-photon-excited fluorescence microscopes ("two-photon fiberscopes"). Two-photon fiberscopes have been developed with the aim of enabling high-resolution imaging of neural activity in freely behaving animals. They use fiber optics to deliver laser light for two-photon excitation. Their small front piece typically contains a miniature scanning mechanism and imaging optics. Two-photon fiberscopes can be made sufficiently small and lightweight to be carried by rats and mice and to allow virtually unrestricted movement within a behavioral arena. Typically mounted to the animal's skull above a cranial window, two-photon fiberscopes permit imaging of cells down to at least 250 µm below the brain surface (e.g., in rat neocortex). In freely exploring animals, action-potential-evoked calcium transients can be imaged in individual somata of visual cortex neurons bulk-labeled with a calcium indicator. Two-photon fiberscopes thus enable high-resolution optical recording of neural activity with cellular resolution during natural behaviors.
authors.forename: Fritjof
authors.initials: F
authors.lastname: Helmchen
authors.forename: Winfried
authors.initials: W
authors.lastname: Denk
authors.forename: Jason N D
authors.initials: JN
authors.lastname: Kerr
mesh_terms: D000818:Animals; D001921:Brain / Q000166:cytology* / Q000502:physiology*; D003584:Cytological Techniques / Q000379:methods*; D008124:Locomotion; D051379:Mice; D036641:Microscopy, Fluorescence, Multiphoton / Q000379:methods*; D008904:Miniaturization / Q000379:methods*; D051381:Rats